The present invention relates to apparatus for cleaning particulate contamination from the surfaces of web substrates; more particularly to cleaning apparatus having one or more particle-attracting (xe2x80x9ccontact cleaningxe2x80x9d) rollers for transferring particulate contamination from a web surface to the surfaces of the rollers; and most particularly, to such apparatus wherein contact between the contact cleaning rollers and the web may be interrupted as desired, and especially when the web is stationary.
It is well known to convey a web substrate around a particle-attracting roller to cause particulate contaminants on the surface of the web substrate to be transferred to the surface of the roller, thereby cleaning the web substrate. Such rollers are known in the art as xe2x80x9ccontact cleaning rollersxe2x80x9d (CCR""s), and may be provided with a tacky surface comprising, for example, adhesive tape as disclosed in U.S. Pat. No. 4,009,047, or an electrostatically-active polymeric surface, for example, a polyurethane as disclosed in U.S. Pat. Nos. 5,611,281 and 5,699,738.
The surface of a contact cleaning roller becomes progressively covered with particles during use, reducing its effectiveness; therefore, the roller surface requires cleaning or xe2x80x9crenewalxe2x80x9d from time to time. Typically, renewal involves the use of liquid agents such as water or solvents to release the particles from the roller surface. Renewal typically leaves the surface of the roller wet for a short time. Experience has shown that if wet renewal is attempted while a CCR is in working (rolling) contact with a substrate, the cleaning fluid can be tracked undesirably onto the substrate. Therefore, various multiple-roller schemes have been proposed to permit engaging a renewed CCR with a web and disengaging a particle-loaded CCR for off-line cleaning while maintaining continuous cleaning of the web substrate. See, for example, the above-cited U.S. Patents, and also U.S. Pat. No. 5,251,348 (""348), the relevant disclosure of which is hereby incorporated by reference.
Patent ""348 discloses an axially rotatable turret disposed transversely of the conveyance path of a web substrate, the turret supporting three equidistantly-spaced contact cleaning rollers adjacent one surface of the web to be cleaned (see FIG. 1 herein). In the rest position of the turret, two rollers are in rolling contact with the moving web, and the third roller is in a cleaning position for renewal. When the third roller has been cleaned and dried, it may be re-engaged with the web as desired by rotating the turret 120xc2x0 to a new rest position, which also brings one of the other two rollers out of contact with the web and into position for cleaning. Thus, renewed rollers may be continually placed back into service as needed without breaking continuity of cleaning contact of the web with one or more contact cleaning rollers.
The ""348 apparatus has been found to present a serious shortcoming when used to clean some delicate web substrates, especially substrates having one or more fragile coatings on the surface being cleaned. When conveyance of the web is stopped and the web is allowed to remain in stationary contact with the contact cleaning rollers for a period of time, the web surface can become adhered to the rollers such that when conveyance is resumed the surface may be stripped from the substrate and remain attached to the rollers, thereby ruining the web for its intended purpose. Even if the substrate surface is not stripped, the adherence can cause a severe web tension imbalance upon an attempt to restart conveyance, resulting in a failure to establish balanced tensions and causing a spontaneous shutdown.
U.S. Pat. No. 5,855,037 discloses a scheme for preventing such adherence and stripping by periodically rotating the turret by a few degrees either clockwise or counterclockwise to bring new portions of the cleaning rollers and web into contact and to break contact between previously-contacting portions thereof before adherence can occur. Such periodic turret rotation can be operationally awkward, and in the extreme, web substrates which adhere very quickly or readily may not be cleaned using this apparatus, which cannot disengage all CCR""s simultaneously from the web under any circumstances. This apparatus can be dangerous to operators, especially if the rotation must be conducted every few seconds. Cleaning or change-out of any of the rollers, or examination or maintenance of the rollers or turret during a conveyance shutdown may be physically impossible or may be precluded by OSHA regulations. Electrical repairs can be difficult or dangerous, or simply impossible, because the turret assembly cannot be shut down electrically and locked out to prevent any spontaneous motion, as is standard practice for such electrical work in known web conveyance systems.
It is a principal object of the invention to provide improved web cleaning apparatus which can a) provide contact with at least one contact cleaning roller during normal operation; b) provide easy cleaning or change-out of every contact cleaning roller in the apparatus; c) provide continuous contact, if desired, with at least one cleaning roller during all periods of web conveyance; and d) disengage all contact cleaning rollers from the web whenever desired, whether the web is being conveyed or is stationary.
It is a further object of the invention to provide improved web cleaning apparatus wherein the apparatus can be stopped mechanically and turned off electrically when fully disengaged from the web substrate.
Briefly described, a system for cleaning particles from a first surface of a web being conveyed along a path includes contact cleaning roller means disposed adjacent to and transverse of the web path. Preferably, such means includes a rotatable turret having first and second end plates and a plurality of rotatable contact cleaning rollers, preferably three rollers positioned equilaterally, disposed between the end plates. The basic web path is positioned with respect to the turret such that, in a non-operative mode, the web is not in contact with any of the cleaning rollers, the web path bypassing the turret. Thus, during periods of maintenance or other downtime, the web first surface is prevented from ferrotyping or other damage which may result from stationary contact with the cleaning rollers. The system further comprises at least one movable backing roller adjacent the second surface of the web, opposite the first surface. Preferably, there are two such backing rollers disposed substantially symmetrically about an axial plane through the turret. To engage the web with the cleaning means into an operative mode, the backing rollers are moved towards the turret to alter the web path such that the web first surface is brought into engagement with the cleaning rollers.